/frontend-react-best-practices

Use Transitions for Non-Urgent Updates

Mark frequent, non-urgent state updates as transitions to maintain UI responsiveness.

Incorrect (blocks UI on every scroll):

function ScrollTracker() {
  let [scrollY, setScrollY] = useState(0);
  useEffect(() => {
    let handler = () => setScrollY(window.scrollY);
    window.addEventListener("scroll", handler, { passive: true });
    return () => window.removeEventListener("scroll", handler);
  }, []);
}

Correct (non-blocking updates):

import { startTransition } from "react";

function ScrollTracker() {
  let [scrollY, setScrollY] = useState(0);
  useEffect(() => {
    let handler = () => {
      startTransition(() => setScrollY(window.scrollY));
    };
    window.addEventListener("scroll", handler, { passive: true });
    return () => window.removeEventListener("scroll", handler);
  }, []);
}